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Caution explaination


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  • 2 weeks later...

CAUTION: The underfloor heat switch must be off

during engine starting and switching of

loads from one generator to another.

Failure to comply could result in a

burned out generator control panel.

Why GCP burn out can some body explain with logic

I don't remember the exact reason, but I seem to remember that this is not an issue with the newer GCU.

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  • 1 month later...

After reading this for the tenth time maybe it is a mix of a few issues.

1. Underfloor heat when ON would use Bleed Air during the start of the first/second engine "and" the Cargo Compartment fan would automatically turn ON as soon as the second generator is put on-line.

2. The second generator voltage should drop initially as the generator assumes the LH and RH AC bus resulting in the VR excitation voltage being increase to bring voltage back up to normal.

3. There is no "start sequence" for the CC fan so all three phases (of the second generator) are supplied to the fan at the same time resulting in a fairly high load. This load increase would happen when the voltage should be trying to stabilize from the initial bus transfer.

4. The larger than normal load of the CC fan would cause the generator voltage to drop even further causing the VR to increase the excitation voltage to the generator to compensate.

5. The excitation voltage travels thru the GCP and that is the connection I see. Increase excitation voltage...

Thats my thought process...

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Thank you for providing Excellent information.Sir you know GCP receive power not more than 7 V such valve that GCP can not burnout ie 3.75 -7.15V

Load applied on Generator not GCP ,Generator should burn out instead of GCP,CC fan load on each phase 5A how?

Munir Abbasi ATI

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My thoughts... Load on the gen (is not the issue) the load on the gen causes the voltage to drop and induces a reaction in the VR thru the GCP so if the VR keeps feeding maximum excitation voltage to the excitation generator (to bring the gen voltage back up) it could cause damage to the GCP.

Fan load is whatever amperage it is. (CBers are rated at 10 AMPs) The "start up" load will be higher than the running load this higher load would occur when the gen voltage is low due to acquiring the LH and RH bus. This would most likely cause the VR to provide the maximum excitation voltage thru the GCP.

Is this the right answer? I do not know but it works for me....

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Thank you for correction i.e CC fan motor CB value 10A.Sir my opinion is Back emf generated by fan motor effect GCP TR unit, it may cause GCP rectifier damage but VR can provides max voltage for exciter field is approximately 7 V. this low power can not damage to any part of GCP i.e GCR



Home of hercules training center Pakistan

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